The invention relates to motor driven compressors used in refrigeration systems. Specifically, the invention relates to preventing the reverse rotation of a motor driving a compressor when a fault condition occurs.
Many compressors are driven by permanent magnet (PM) motors. PM motors act as generators when their rotors are driven by external forces and not by their stators. Pressure of a refrigerant in a refrigeration system can cause a compressor to rotate in a reverse direction when a fault occurs. This reverse rotation of the compressor results in the PM motor becoming a generator. If the reverse rotation is significant enough, the PM motor can produce voltage and current having magnitudes sufficient to damage components of the motor and/or control system.